Vaccine safety


Strict procedures are followed when vaccines are made. Before a vaccine can be licensed for use it goes through a long testing process by international scientists to check that it is safe, and that it works. This process usually takes several years and includes trials on people who volunteer to use it. Before a vaccine is approved for supply in New Zealand the manufacturer must demonstrate its quality, that it works well and that it is safe to the satisfaction of Medsafe, a division of the Ministry of Health.

Medsafe’s evaluation is performed to internationally defined standards and is based on data from clinical trials.

The gold standard for clinical trials includes three phases:

Phase 1:

Small numbers of people take the same vaccine using different methods of delivery and/or dosage. Assesses safety and immune response.

Phase 2:

Uses larger numbers of people and compares new treatments with a placebo. Continues to assess safety and immune response.

Phase 3:

Large, randomised trial(s) to test the effect of a new vaccine against a control group. This phase tests safety and efficacy, which is the percentage of people that the vaccine protects from catching the disease.


Once a vaccine has been introduced to New Zealand, the Centre for Adverse Reactions Monitoring (CARM) at Otago University records reactions reported after vaccination.

Vaccinators are asked to report all clinically significant events following vaccination to CARM.

Parents may also report and ask for advice on serious reactions by ringing CARM on 03 479 7247. The information provided to CARM by doctors, nurses and parents will assist in identifying those children who should receive follow-up immunisation in a controlled environment, such as a hospital.

Mild reactions such as mild fever, pain, or redness where the injection was given are not reported to CARM.

Any serious reactions may also be recorded on the National Immunisation Register (NIR)

Parents should contact their doctor or Healthline (phone 0800 611 116) if they are worried about their child following immunisation.


Studies have shown that if all doses of vaccines are given they will protect 80–95 percent of the children who are immunised. For example, the pertussis (whooping cough) vaccine is effective in 84 percent of children and measles vaccine in 90–95 percent of children.

A very small number of children who are immunised do not develop strong immunity and they may still become ill with one of the diseases. If that happens they usually have a milder illness than people who have not been immunised. More than one dose of some vaccines is needed for full protection. Booster doses may also be required in later years to maintain protection, eg, tetanus.

Community immunity is an important part of protecting the community against disease. People who have not been immunised are often protected because most immunised people do not get sick from an illness they are vaccinated against. This prevents infection from circulating and helps to prevent an unimmunised person from becoming infected.

Concerns about immunisation

Some people have concerns about immunisation, ranging from questions about the need to vaccinate when a disease is not common or serious, to issues about the safety and efficacy of vaccines.

For more information, to the Immunisation Handbook  and the following websites:

Articles relating to immunisation


National Centre for Immunisation Research and Surveillance, Australia

Centre for Disease Control and Prevention, USA


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